Woven fabrics having heat-shrinkable yarns incorporated therein are well known. For example, at least three patents to B. H. Foster in the early 1950's (U.S. Pat. Nos. 2,627,644, 2,635,648, and 2,771,661) and one to McCord in 1956 (U.S. Pat. No. 2,757,434) use heat-shrinkable yarns along with non-heat-shrinkable yarns to make honeycombed, puffed and/or corrugated fabrics for use in bedding, clothing and the like.
In addition, woven fabrics having the same or similar general cuspated profile or "honeycomb" type weave configuration as the present invention are known in the art and are used as tower packing and/or as the separation medium in mist eliminators. For instance, Pedersen U.S. Pat. No. 4,022,596 relates to a fluid treating medium through which fluid may pass for removing particulate material from the fluid. The material used is comprised of at least two sets of strands interleaved together in a particular configuration to each other so that the strands extending in one direction are generally straight while the strands extending in another direction are geometrically arranged so as to provide a fabric having a cuspated configuration or profile. The fabric of the present invention is similar in profile except it may bend the strands of yarn in both directions.
Nevertheless, other fabrics do in fact have similar configurations or profiles. However, they are typically used in mist eliminators and other apparatus where separation medium of this type may be required. At least one such fabric is available from the Lumite Division of Synthetic Industries of Gainesville, Ga. Notably, however, none of these fabrics have ever been used for soil retention and stabilization or turf reinforcement. Significantly, this is because the yams used to make these fabrics are not strong enough or do not form fabrics which are thick and durable enough or dimensionally stable enough to withstand the extremely rugged conditions exhibited within soil embankments and the like. In other words, these fabrics are not high-profile structures. A high-profile structure has a thickness considerably greater than that of an ordinary "honeycomb" woven fabric. It is this thickness in combination with the strength and dimensional stability of the fabric which permits the fabric to restrain the movement of soil or gravel filling the space defined by the fabric on a steep slope or embankment.
Also of major importance to the use of fabrics in soil design and performance are weight, strength, and modulus. It is a combination of these properties, including thickness, which determines whether a geotextile fabric will be suitable for use in soil retention and stabilization as well as turf reinforcement. Desirably, a fabric having a typical tensile strength of at least about 3200.times.2400 pounds per foot (warp.times.fill, respectively) as determined by the American Society for Testing and Materials' (ASTM) Standard Test Method D4595, a modulus of at least about 10000 pounds per foot determined by ASTM D4595 at 10 percent elongation, and a thickness of at least about 500 mils (0.5 inches) determined by ASTM D1777 is necessary to provide soil stabilization and erosion control on slopes, embankments, subgrades and veneer layers in places such as landfills. While some mattings and other similar structures have, heretofore, been used to aid in soil retention or erosion control, most of these structures have been generally ineffective in providing true stability and reinforcement for the soil. In fact, most of the prior art structures have employed generally straight yarns in at least one direction, are not heat-shrinkable, and/or have filaments which are melt-bonded together so as to cause failure points to exist with respect to the bonding of the fabric.
For example, Daimler et al. U.S. Pat. No. 3,934,421 discloses a matting comprising a plurality of continuous amorphous synthetic thermoplastic filaments which are bonded together at their intersections and can be used for the ground stabilization of road beds.
Murhling et al. U.S. Pat. No. 4,002,034 is directed toward a multi-layered matting for inhibiting the erosion of an embankment around a body of water, the layer closest to the water having less pore space and thinner fibers than the layers away from the water.
Bronner U.S. Pat. No. 4,329,392 discloses a hydraulic engineering matting for inhibiting rearrangement of soil particles comprising a layer of melt-spun synthetic polymer filaments bonded at their points of intersection, a filter layer of fine fibers bonded thereto, and a third layer interdispersed therethrough.
Ter Burg et al. U.S. Pat. No. 4,421,439 discloses a supporting fabric or matting for use on embankments of roads, dikes, and the like. The fabric generally includes straight yarns in both the warp and weft directions with binder yams extending in the warp direction and woven around the straight yarns of the weft direction. However, these yams do not impart strength to the straight yarns.
Leach U.S. Pat. No. 4,472,086 is directed toward a geotextile fabric for erosion control having uncrimped synthetic threads in both the warp and filling directions and a known yarn stitch bonding the warp and filling threads together.
Finally, a commercially known high-profile structure generally used for soil retention and erosion control which does employ heat-shrinkable yarns, but not in a single layer, is disclosed in Stancliffe et al. U.S. Pat. No. 4,762,581. This patent relates to high-profile structures or composites which are noted to be useful as carpet underlay and mattresses as well as embankment stabilization and drainage. These structures are believed to be commercially sold under the tradename, Tensar, and are available from Netlon Limited of Mill Hill, England.
However, the structures in Stancliffe et al. are provided by the welding of a planar, biaxially heat-shrinkable, plastic mesh layer to a planar, relatively non-heat-shrinkable plastic mesh layer at zones which are spaced apart on a generally square grid. Hence, when the heat-shrinkable layer is heated and shrinks, the non-heat-shrinkable layer assumes a generally cuspated configuration with the welded points on the non-heat-shrinkable layer remaining in contact with the heat-shrinkable layer. This patent does not provide a single layer fabric and is susceptible to failure at the welding points bonding the layers together.
Thus, while attempts have been made heretofore to provide a suitable means for stabilizing and retaining soil and for reinforcing turf, the art has not provided a facile means by which to do so. Accordingly, a need clearly exists for a single-layered, high-profile, three-dimensional, homogeneous fabric comprising fibers of differing heat shrinkage characteristics which will increase dimensional stability and last longer than other high-profile structures commonly utilized for soil retention and vegetative reinforcement.